75 lines
2.1 KiB
Python
75 lines
2.1 KiB
Python
"""
|
|
Not all output rates are going to be supported by the system sound card.
|
|
Choosing from a limited subset of preferred output rates is how we guarantee
|
|
that the system will be able to play the output audio.
|
|
Sample rates stolen from:
|
|
https://en.wikipedia.org/wiki/Sampling_(signal_processing)
|
|
"""
|
|
supported_ouput_rates = [
|
|
8000, # Telephone, P25 audio (sufficient for speech, some consonants unintelligble)
|
|
16000, # Modern telephone/VoIP, good quality speech
|
|
32000, # FM radio
|
|
44100, # CD audio quality
|
|
48000,
|
|
50000, # Uncommon but supported
|
|
88200,
|
|
96000, # DVD/Blu-ray audio
|
|
192000, # Too much.
|
|
]
|
|
|
|
|
|
def score(pair, target_output=32000, target_ratio=10):
|
|
"""
|
|
Heuristic for scoring input & output sample rates. The criteria are:
|
|
- closest to 44.1 kHz is better;
|
|
- closer to a ratio of 10 is better,
|
|
- additionally penalising ratios lower than 10.
|
|
|
|
Lower scores are better.
|
|
|
|
This should result in selected sample rates that give good audio quality
|
|
without wasting CPU cycles on a needlessly high input rate.
|
|
"""
|
|
|
|
# Give the worst score possible for impossible pairs.
|
|
if pair[0] % pair[1] != 0:
|
|
return float("inf")
|
|
|
|
ratio = pair[0] // pair[1]
|
|
|
|
return (
|
|
abs(pair[1] - target_output) / 2500
|
|
+ max(0, target_output - pair[1]) / 2500
|
|
+ abs(ratio - target_ratio) ** 0.8
|
|
+ max(0, target_ratio - ratio) ** 2
|
|
)
|
|
|
|
|
|
def flatten(l):
|
|
return [item for sublist in l for item in sublist]
|
|
|
|
|
|
def flatten_dict(d):
|
|
return [(key, value) for key, rates in d.items() for value in rates]
|
|
|
|
|
|
def get_pairs(input_rate):
|
|
return [
|
|
(input_rate, rate) for rate in supported_ouput_rates if (input_rate % rate == 0)
|
|
]
|
|
|
|
|
|
def supported_sample_rates(supported_input_rates):
|
|
return {
|
|
in_rate: [
|
|
out_rate for out_rate in supported_ouput_rates if in_rate % out_rate == 0
|
|
]
|
|
for in_rate in supported_input_rates
|
|
}
|
|
|
|
|
|
def preferred_sample_rates(supported_input_rates):
|
|
return sorted(
|
|
flatten_dict(supported_sample_rates(supported_input_rates)), key=score
|
|
)
|